Instrumental (operant) behavior can be goal directed, but after extended practice it can become a habit triggered by environmental stimuli. There is little information, however, about the variables that encourage habit learning, or about the development of discriminated habits that are actually triggered by specific stimuli. (Most studies of habit in animal learning have used free-operant methods.) In the present experiments, rats received training in which a lever press was reinforced only in the presence of a discrete stimulus (S) and the status of the behavior as goal-directed or habitual was determined by reinforcer devaluation tests. Experiment 1 compared lever insertion and an auditory cue (tone) in their ability to support habit learning. Despite prior speculation in the literature, the "salient" lever insertion S was not better than the tone at supporting habit, although the rats learned more rapidly to respond in its presence. Experiment 2 then examined the role of reinforcer predictability with the brief (6-s) tone S. Lever pressing during the tone was reinforced on either every trial or on 50% of trials; habit was observed only with the highly predictable (100%) relationship between S and the reinforcer. Experiment 3 replicated this effect with the tone in a modified procedure and found that lever insertion contrastingly encouraged habit regardless of reinforcer predictability. The results support an interactive role for reinforcer predictability and stimulus salience in discriminated habit learning.

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Nicotine promotes interoceptive changes in the nervous system. Such interoceptive stimuli play important roles in modulating addictive behavior. Operant and Pavlovian stimulus control modulate responsiveness to environmental stimuli related to drug-seeking and self- administration. Nicotine functions as a discriminative stimulus in modulating operant behavior as well as Pavlovian feature stimuli in modulating the conditional responding (CR) to exteroceptive CSUS contingencies. Elucidation of the interaction of these interoceptive stimulus control functions is vital for a comprehensive understanding of nicotine use/abuse,which might lead to better behavioral treatment strategies. This experiment evaluated the interaction among Pavlovian feature positive (FP) and feature negative (FN) effects of nicotine on concurrently occurring operant SD and SD effects. Sixteen rats were trained in a Pavlovian and operant bidirectional contingency paradigm, using nicotine (0.3 mg/kg) and non-drug (saline) states as interoceptive cues for operant discriminative stimulus conditions (SD and S∆) as well as Pavlovian FP and FN for a light-CS, either leading to a shared food pellet outcome or non-outcome. Nicotine and saline sessions were intermixed. For one group of rats (n=8), nicotine served as an SD for lever pressing (variable interval 60 sec) and simultaneously functioned as an FN for CS-lightnoUS relation on the same sessions. On intermixed sessions, saline served as the SDfor lever pressing (non-reinforced) and FP, during which the 8-sec light preceded delivery of the food pellet (variable time ITI = 60 sec). For the other group (n=8) nicotine served as the SD (lever pressing non-reinforced) and FP for the CS, with saline serving in the reverse roles. Consecutive brief non-reinforcement tests revealed that: A) rates of lever pressing were significantly greater in S than SD with nicotine and saline suggesting strong operant discriminative stimulus control; B) FP responding to the light CS with nicotine and saline was evident; and C) FN suppression of the CR with nicotine was not evident but weak under saline. These data suggest that nicotine can function as an interoceptive context that hierarchically can enter into concurrently opposing modulatory relations in Pavlovian and operant drug discrimination procedures.